A manipulator-type industrial robot (hereinafter referred to as a robot) generally contains electric cables, fluid pipes for supplying air or gas, and the like. These cables and pipes are used in a motor driving joint axes of a manipulator, a welding feeder device mounted on the manipulator, and peripheral devices, such as various kinds of sensors and a handling holder device.
The electric cables are connected to control devices or external devices such as a welding power supply at a connector. A cable opening is disposed in a connection case of a manipulator base section. Specifications for, and the number of the signal lines of the electric cables that connect between the manipulator and the control devices, are determined by a motor that drives joint axes of the manipulator. On the other hand, the signal lines of the electric cables that connect the manipulator to the external devices including a welding power supply vary in specifications and quantity because peripheral devices to be mounted on the manipulator depend on the use of the robot.
The cables routed through the inside of the manipulator undergo bending or torsion caused by rotating motions of the joints of the manipulator. The need for mechanical durability imposes limitations on the specifications and quantity of the signal lines. In other words, due to the limitation, the cables routed inside the manipulator cannot be simply increased in diameter or quantity.
As for cable connection at a connection case of a manipulator, a method in which a split connector is used for one frame, as shown in FIG. 9A and FIG. 9B, is conventionally known. The method, for example, is disclosed in Japanese Patent Unexamined Publication No. H11-129185.
FIG. 9A is a sectional view illustrating an essential part of the interior of the connection case of a conventional robot. FIG. 9B is a sectional view of a conventional split connector shown in FIG. 9A. Internal cable 8 is inserted through opening 13 of base 2 of the robot. Split connector 15 is disposed in hole 14 formed in base 2. Split connector 15 has frame 16 and housing 17. Frame 16 has five slots 16a in a row, each of which contains a housing 17, such that five housings 17 are accommodated in frame 16. Wires 12 of internal cable 8 are connected to each of four terminal fittings 17a; twenty wires 12 are connected to split connector 15 in all. Besides, second connector 10, which is disposed outside base 2, is removably connected to split connector 15. Second connector 10 further has a connection to external cable 7 connected to an external device. The connection relationship between external cable 7 and internal cable 8 via wires 12 and split connector 15 has a one-to-one correspondence, that is, a fixed connection.
According to the structure above, a split connector is disposed at one end of an electric cable routed through the inside of the manipulator. The use of the split connector allows a through-hole for passing cables to the connection case to be made small, whereby the connection case can be decreased in size. However, the signal connection between the internal cable and the external cable remains one-to-one correspondence (fixed) relation. Due to this constraint, when a control device with a built-in welding power supply as an external device is connected to the manipulator, the manipulator needs cable connections not only for the control device, but also for the power supply. This causes an increase in the number of external cables connecting between the manipulator and the control device.
In a case where the control device and the welding power supply are separately connected to the manipulator, some kind of welding feeder device mounted on the manipulator or peripheral devices such as a sensor require that the signal cables of the peripheral devices should be separately connected to the control device and the welding feeder device. The cables therefore must be separated outside the manipulator.
In another case where a peripheral device, such as a sensor, is disposed close to the manipulator, the signal cable of the peripheral device needs to have an additional cable connection to a control device.
As described above, specifications for signal lines and connections largely depend on the use of the robot. The fixed signal-connection (i.e., one-to-one correspondence) between the internal cable and the external cable causes an increase in the number of external cables or the need for cable separation outside the manipulator. This inconvenience has invited complicated routing of the external cables, has increased the space occupied by the cables, and has increased production costs.